1. Field of the Invention
This invention relates to a wafer grinding method for grinding the back surface of a wafer held by suction and a wafer grinding machine for carrying out the grinding method.
2. Description of the Related Art
In the field of semiconductor manufacturing, wafers tend to become larger year by year and the wafers are made thinner in order to increase packing density. In order to make a semiconductor wafer thinner, a backgrinding process for grinding a back surface of the wafer is performed. Japanese Unexamined Patent Publication No. 2000-21952, for example, discloses a technique for grinding the back surface of the wafer by holding the wafer by adsorption in a chuck using the sucking force of the vacuum.
FIG. 5 is a schematic diagram showing the wafer grinding machine according to the prior art as disclosed in Japanese Unexamined Patent Publication No. 2000-21952. At the time of grinding the back surface of the wafer, a surface protection film 11 is attached on the front surface 41 of the wafer 40. This surface protection film 11 protects the circuit patterns (not shown) formed on the front surface 41. As shown in FIG. 5, the wafer 40 is held by adsorption to an adsorption unit 260 with the back surface 42 directed up.
As indicated by solid arrows in FIG. 5, the grinding fluid is supplied to the contact point between a grinding stone 280 and the wafer 40, which are rotated with each other.
The greater part of the grinding fluid is supplied to the back surface 42 of the wafer 40. However, as shown in FIG. 5, part of the grinding fluid impinges directly on the boundary 45 between the front surface 41 and the front surface protection film 11 of the wafer 40. As a result, as shown in the partial sectional view of FIG. 6 showing the conventional wafer grinding machine, the surface protection film 11 is separated from the edge of the wafer 40.
In such a case, the grinding fluid flows into the gap between the wafer 40 and the surface protection film 11 and may foul the circuit pattern on the front surface 41 of the wafer 40. When the grinding fluid flows further into the gap, the surface protection film 11 is further separated. As a result, the wafer 40 may come off from the adsorption unit 260 with the front surface protection film 11 held by the adsorption unit 260.
This invention has been achieved in view of this situation, and the object thereof is to provide a wafer grinding method capable of preventing the surface protection film from being separated from the wafer at the time of grinding the back surface of the wafer and a wafer grinding machine for carrying out the method.